The present invention relates to an optoelectronic photocoupler device, comprising, opposite to each other in approximately parallel planes, a light emitter and a photosensitive receiver, both having semiconductor crystals the emitter and the receiver are coupled optically along an axis which is substantially perpendicular to the said planes and each is connected to electric connections. The photocoupler device further comprises a shield for providing electric insulation between the light emitter and the receiver the principal plane of the shield being perpendicular to the optical axis.
Such a photocoupler device is applicable notably in telephony.
Several opto-electronic combinations are known which are composed of an emitter and a receiver which are coupled optically so as to transfer electric information from the emitter to the said receiver through a light signal.
From a mechanical point of view, the assembly which is most current up till now consists of assembling face to face the light emitter and the said light receiver connected by a transparent resin, while ensuring that they are situated on the same optical axis perpendicular to the planes of the light emissive and the light sensitive faces.
In general, an electroluminescent semiconductor diode is used as an emitter and a photodiode, a phototransistor, or a photoresistor is used as a receiver.
From the electrical point of view, it is necessary to determine an optimum distance between the emitter and the receiver since this affects both the value of the transfer function and the value of the isolation.
In a photocoupler device the value of the insulation between the emitter and the receiver is a fundamental characteristic related not only to the distance which they are separated, but also to the distance which separates the connection wires and to the quality of the interstitial insulations.
During the assembly of the light emitter and the light receiver it is necessary to keep the connection wires spaced apart. However, there always remains a fair chance that these two wires will be comparatively close together, which may be due to the topology of the emitter and/or the receiver or even due to the length of the wires. In this case, the proximity of two wires results in a zone of low impedance. In addition the transparent resin, which is chosen to ensure optical transmission, and electrical insulation may, contain a certain number of defects. The resin may notably be influenced by reversion phenomena or depolymerisation phenomena due probably to the confinement in an evacuated space. The phenomenon of ionization may also be mentioned which characterizes certain resins containing either impurities such as hydrolysable chlorine, or metallic ions, or certain resins presenting a molecular lattice which is too wide to stop a diffusion of external impurities.
In addition, numerous devices operate in difficult current and/or voltage conditions. This is the case notably with devices used in the automobile industry. The components constituting these devices are then subjected to thermal and electrical strains which produce mechanical and electrical disturbances.
In order to meet these types of disadvantages an insulating element has already been used in the form of a shield interposed between the light emitter and the light receiver.
Such a shield used notably in photocouplers produced by the Societe General Electric consists of by a thin sheet of glass adhered, by means of a silicon resin, to metallic surfaces deposited on semiconductor crystals in which the emitter and the receiver have been produced.
This solution still presents several disadvantages. In fact, due to the difference between their coefficients of expansion, the adhesion between the glass sheet and the layer of resin is not easy to produce and is not reliable. So, if faults are produced at the level of the interface between the sheet and the resin layer, these faults provide as many paths for stray leakage currents. Moreover, the manipulation of the sheet and its assembly between the emitter and the receiver is difficult considering the small dimensions of the sheet and its fragility. For reasons of light transfer efficiency it is necessary for the dimensions of the sheet to remain small, in particular as regards its thickness.
Moreover, the sheet of glass does not easily dissipate the heat accumulated in the photocoupler device. This heat is produced notably by the operation of the light source.